<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    div {
      width: 100px;
      height: 100px;
      background-color: #f00;
    }

    .box {
      background-color: green;
      /* 
      上 右 下 左
      1 margin: 10px;  
      2 margin: 10px  50px 
      3 margin: 10px  50px  10px  
      3 margin: 10px 50px 80px 50px 
       */
      margin: 10px 50px 80px 40px;
    }
  </style>
</head>

<body>
  <!-- div*3 -->
  <!-- div{$}*3 -->
  <div>1</div>
  <div class="box">2</div>
  <div>3</div>

</body>

</html>